The present invention relates to a novel process for preparing polyolefins. More particularly, the present invention relates to a process for preparing polyolefins of good particles having a large average particle diameter and a narrow molecular weight distribution, which process is capable of greatly increasing the polymer yield per solid and that per transition metal, thereby permitting the omission of the step of removing catalyst remaining in the resulting polymer, further capable of increasing the bulk density of the polymer and decreasing a fine particulate portion of the polymer.
Heretofore, in this technical field there have been known many catalysts comprising inorganic magnesium solids as carriers such as magnesium halide, magnesium oxide and magnesium hydroxide and a transition metal compound such as a titanium compound or a vanadium compound supported on the carriers. However, the polyolefins obtained in the prior art are generally low in bulk density, relatively small in average particle diameter and generally wide in particle size distribution so contain a large proportion of fine particles. Besides, when these powdery polymers are subjected to forming, there arise problems such as dusting and lowering of the forming, efficiency. For the reason, improvement has keenly been desired from the standpoint of productivity and polymer handling. Further, still further improvements are considered necessary in order to satisfy the recent keen desire for omitting the pelletizing step and using a powdery polymer directly in a processing machine.
The present inventors have previously found out novel catalyst components with the above drawbacks remedied and already filed patent applications thereon (see JP1-11651B, 1-12289B, 60-149605A, 62-32105A and 62-207306A). The use of these catalyts component can afford a polymer having a high bulk density and a large average particle diameter. However, a further improvement has been considered necessary for omitting the pelletizing step and using a powdery polymer directly in a processing machine.
Also, there are various fields in which a polyolefin having a narrow molecular weight distribution is required. For example, an injection-grade polyolefin requires a narrow molecular weight to improve the impact strength and a film-grade polyolefin to improve the strength, transparency, anti-blocking property and heat-sealability.
The present inventors have also found out catalyst components having such properties and filed patent applications (see JP3-64306A, 3-153707A, 3-185004A, 3-252407A and 2-179485A). These catalyst components can each afford a polymer having a narrow molecular weight has still been required.
It is the object of the present invention to remedy the above-mentioned drawbacks and obtain in extremely high activity a polymer having a high bulk density, a narrow particle size distribution, an extremely proportion of fine particles, and superior in fluidity.